cpuidle: riscv-sbi: Use scoped device node handling to fix missing of_node_put

cpuidle: riscv-sbi: Use scoped device node handling to fix missing of_node_put

Two return statements in sbi_cpuidle_dt_init_states() did not drop the
OF node reference count.  Solve the issue and simplify entire error
handling with scoped/cleanup.h.

Fixes: 6abf32f1d9c5 ("cpuidle: Add RISC-V SBI CPU idle driver")
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://patch.msgid.link/20240820094023.61155-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>